This enzyme belongs to the family of oxidoreductases, specifically those acting on paired donors, with O2 as oxidant and incorporation or reduction of oxygen. The oxygen incorporated need not be derived from O2 with NADH or NADPH as one donor, and incorporation of one atom o oxygen into the other donor. The systematic name of this enzyme class is (S)-limonene,NADPH:oxygen oxidoreductase (7-hydroxylating). Other names in common use include (-)-limonene 7-monooxygenase, (-)-limonene hydroxylase, (-)-limonene monooxygenase, and (-)-limonene,NADPH:oxygen oxidoreductase (7-hydroxylating). This enzyme participates in monoterpenoid biosynthesis and limonene and pinene degradation. It employs one cofactor, heme.

1.
Chemical reaction
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A chemical reaction is a process that leads to the transformation of one set of chemical substances to another. Nuclear chemistry is a sub-discipline of chemistry that involves the reactions of unstable. The substance initially involved in a reaction are called reactants or reagents. Chemical reactions are characterized by a chemical change, and they yield one or more products. Reactions often consist of a sequence of individual sub-steps, the elementary reactions. Chemical reactions are described with chemical equations, which present the starting materials, end products. Chemical reactions happen at a characteristic reaction rate at a given temperature, typically, reaction rates increase with increasing temperature because there is more thermal energy available to reach the activation energy necessary for breaking bonds between atoms. Reactions may proceed in the forward or reverse direction until they go to completion or reach equilibrium, Reactions that proceed in the forward direction to approach equilibrium are often described as spontaneous, requiring no input of free energy to go forward. Non-spontaneous reactions require input of energy to go forward. Different chemical reactions are used in combinations during chemical synthesis in order to obtain a desired product, in biochemistry, a consecutive series of chemical reactions form metabolic pathways. These reactions are catalyzed by protein enzymes. Chemical reactions such as combustion in fire, fermentation and the reduction of ores to metals were known since antiquity, in the Middle Ages, chemical transformations were studied by Alchemists. They attempted, in particular, to lead into gold, for which purpose they used reactions of lead. The process involved heating of sulfate and nitrate minerals such as sulfate, alum. In the 17th century, Johann Rudolph Glauber produced hydrochloric acid and sodium sulfate by reacting sulfuric acid, further optimization of sulfuric acid technology resulted in the contact process in the 1880s, and the Haber process was developed in 1909–1910 for ammonia synthesis. From the 16th century, researchers including Jan Baptist van Helmont, Robert Boyle, the phlogiston theory was proposed in 1667 by Johann Joachim Becher. It postulated the existence of an element called phlogiston, which was contained within combustible bodies. This proved to be false in 1785 by Antoine Lavoisier who found the explanation of the combustion as reaction with oxygen from the air

2.
Oxygen
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Oxygen is a chemical element with symbol O and atomic number 8. It is a member of the group on the periodic table and is a highly reactive nonmetal. By mass, oxygen is the third-most abundant element in the universe, after hydrogen, at standard temperature and pressure, two atoms of the element bind to form dioxygen, a colorless and odorless diatomic gas with the formula O2. This is an important part of the atmosphere and diatomic oxygen gas constitutes 20. 8% of the Earths atmosphere, additionally, as oxides the element makes up almost half of the Earths crust. Most of the mass of living organisms is oxygen as a component of water, conversely, oxygen is continuously replenished by photosynthesis, which uses the energy of sunlight to produce oxygen from water and carbon dioxide. Oxygen is too reactive to remain a free element in air without being continuously replenished by the photosynthetic action of living organisms. Another form of oxygen, ozone, strongly absorbs ultraviolet UVB radiation, but ozone is a pollutant near the surface where it is a by-product of smog. At low earth orbit altitudes, sufficient atomic oxygen is present to cause corrosion of spacecraft, the name oxygen was coined in 1777 by Antoine Lavoisier, whose experiments with oxygen helped to discredit the then-popular phlogiston theory of combustion and corrosion. One of the first known experiments on the relationship between combustion and air was conducted by the 2nd century BCE Greek writer on mechanics, Philo of Byzantium. In his work Pneumatica, Philo observed that inverting a vessel over a burning candle, Philo incorrectly surmised that parts of the air in the vessel were converted into the classical element fire and thus were able to escape through pores in the glass. Many centuries later Leonardo da Vinci built on Philos work by observing that a portion of air is consumed during combustion and respiration, Oxygen was discovered by the Polish alchemist Sendivogius, who considered it the philosophers stone. In the late 17th century, Robert Boyle proved that air is necessary for combustion, English chemist John Mayow refined this work by showing that fire requires only a part of air that he called spiritus nitroaereus. From this he surmised that nitroaereus is consumed in both respiration and combustion, Mayow observed that antimony increased in weight when heated, and inferred that the nitroaereus must have combined with it. Accounts of these and other experiments and ideas were published in 1668 in his work Tractatus duo in the tract De respiratione. Robert Hooke, Ole Borch, Mikhail Lomonosov, and Pierre Bayen all produced oxygen in experiments in the 17th and the 18th century but none of them recognized it as a chemical element. This may have been in part due to the prevalence of the philosophy of combustion and corrosion called the phlogiston theory, which was then the favored explanation of those processes. Established in 1667 by the German alchemist J. J. Becher, one part, called phlogiston, was given off when the substance containing it was burned, while the dephlogisticated part was thought to be its true form, or calx. The fact that a substance like wood gains overall weight in burning was hidden by the buoyancy of the combustion products

3.
Water
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Water is a transparent and nearly colorless chemical substance that is the main constituent of Earths streams, lakes, and oceans, and the fluids of most living organisms. Its chemical formula is H2O, meaning that its molecule contains one oxygen, Water strictly refers to the liquid state of that substance, that prevails at standard ambient temperature and pressure, but it often refers also to its solid state or its gaseous state. It also occurs in nature as snow, glaciers, ice packs and icebergs, clouds, fog, dew, aquifers, Water covers 71% of the Earths surface. It is vital for all forms of life. Only 2. 5% of this water is freshwater, and 98. 8% of that water is in ice and groundwater. Less than 0. 3% of all freshwater is in rivers, lakes, and the atmosphere, a greater quantity of water is found in the earths interior. Water on Earth moves continually through the cycle of evaporation and transpiration, condensation, precipitation. Evaporation and transpiration contribute to the precipitation over land, large amounts of water are also chemically combined or adsorbed in hydrated minerals. Safe drinking water is essential to humans and other even though it provides no calories or organic nutrients. There is a correlation between access to safe water and gross domestic product per capita. However, some observers have estimated that by 2025 more than half of the population will be facing water-based vulnerability. A report, issued in November 2009, suggests that by 2030, in developing regions of the world. Water plays an important role in the world economy, approximately 70% of the freshwater used by humans goes to agriculture. Fishing in salt and fresh water bodies is a source of food for many parts of the world. Much of long-distance trade of commodities and manufactured products is transported by boats through seas, rivers, lakes, large quantities of water, ice, and steam are used for cooling and heating, in industry and homes. Water is an excellent solvent for a variety of chemical substances, as such it is widely used in industrial processes. Water is also central to many sports and other forms of entertainment, such as swimming, pleasure boating, boat racing, surfing, sport fishing, Water is a liquid at the temperatures and pressures that are most adequate for life. Specifically, at atmospheric pressure of 1 bar, water is a liquid between the temperatures of 273.15 K and 373.15 K

4.
Catalysis
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Catalysis is the increase in the rate of a chemical reaction due to the participation of an additional substance called a catalyst. In most cases, reactions occur faster with a catalyst because they require less activation energy, furthermore, since they are not consumed in the catalyzed reaction, catalysts can continue to act repeatedly. Often only tiny amounts are required in principle, in the presence of a catalyst, less free energy is required to reach the transition state, but the total free energy from reactants to products does not change. A catalyst may participate in multiple chemical transformations, the effect of a catalyst may vary due to the presence of other substances known as inhibitors or poisons or promoters. Catalyzed reactions have an activation energy than the corresponding uncatalyzed reaction, resulting in a higher reaction rate at the same temperature. However, the mechanics of catalysis is complex. Usually, the catalyst participates in this slowest step, and rates are limited by amount of catalyst, in heterogeneous catalysis, the diffusion of reagents to the surface and diffusion of products from the surface can be rate determining. A nanomaterial-based catalyst is an example of a heterogeneous catalyst, analogous events associated with substrate binding and product dissociation apply to homogeneous catalysts. Although catalysts are not consumed by the reaction itself, they may be inhibited, deactivated, in heterogeneous catalysis, typical secondary processes include coking where the catalyst becomes covered by polymeric side products. Additionally, heterogeneous catalysts can dissolve into the solution in a system or sublimate in a solid–gas system. The production of most industrially important chemicals involves catalysis, similarly, most biochemically significant processes are catalysed. Research into catalysis is a field in applied science and involves many areas of chemistry, notably organometallic chemistry. Catalysis is relevant to aspects of environmental science, e. g. the catalytic converter in automobiles. Many transition metals and transition metal complexes are used in catalysis as well, Catalysts called enzymes are important in biology. A catalyst works by providing a reaction pathway to the reaction product. The rate of the reaction is increased as this route has a lower activation energy than the reaction route not mediated by the catalyst. The disproportionation of hydrogen peroxide creates water and oxygen, as shown below,2 H2O2 →2 H2O + O2 This reaction is preferable in the sense that the reaction products are more stable than the starting material, though the uncatalysed reaction is slow. In fact, the decomposition of hydrogen peroxide is so slow that hydrogen peroxide solutions are commercially available and this reaction is strongly affected by catalysts such as manganese dioxide, or the enzyme peroxidase in organisms

5.
Methane monooxygenase
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Methane monooxygenase, or MMO, is an enzyme capable of oxidizing the C-H bond in methane as well as other alkanes. Methane monooxygenase belongs to the class of oxidoreductase enzymes, there are two well-studied forms of MMO, the soluble form and the particulate form. The active site in sMMO contains a di-iron center bridged by an atom, whereas the active site in pMMO utilizes copper. Structures of both proteins have been determined by X-ray crystallography, however, the location and mechanism of the site in pMMO is still poorly understood and is an area of active research. These enzymes have a relatively wide substrate specificity and can catalyse the oxidation of a range of substrates including ammonia, methane, halogenated hydrocarbons and these enzymes are composed of 3 subunits - A, B and C - and contain various metal centers, including copper. The A subunit from Methylococcus capsulatus resides primarily within the membrane and consists of 7 transmembrane helices and a beta-hairpin, a conserved glutamate residue is thought to contribute to a metal center. Methane monooxygenases are found in bacteria, a class of bacteria that exist at the interface of aerobic and anaerobic environments. One of the widely studied bacteria of this type is Methylococcus capsulatus. This bacterium was discovered in the hot springs of Bath, England, methanotrophic bacteria play an essential role of cycling carbon through anaerobic sediments. The chemistry behind the cycling takes a chemically inert hydrocarbon, methane, other hydrocarbons are oxidized by MMOs, so a new hydroxylation catalyst based on the understanding of MMO systems could possibly make a more efficient use of the world supply of natural gas. This is a monooxygenase reaction in which two reducing equivalents from NADH are utilized to split the O-O bond of O2. The best characterized forms of soluble MMO contains three components, hydroxylase, the β unit, and the reductase. Each of which is necessary for effective substrate hydroxylation and NADH oxidation, X-ray crystallography of the MMO shows that it is a dimer formed of three subunits, α2β2γ2. With 2.2 A resolution, the shows that MMO is a relatively flat molecule with the dimensions of 60 x 100 x 120 A. In addition, there is a wide canyon running along the interface with an opening in the center of the molecule. Most of the protomers involves helices from the α and β subunits with no participation from the γ subunit, also, the interactions with the protomers resembles ribonucleotide reductase R2 protein dimer interaction, resembling a heart. Each iron has a six coordinate octahedral environment, the dinuclear iron centers are positioned in the α subunit. The substrate must bind near the site in order for the reaction to take place

6.
Cholesterol 7 alpha-hydroxylase
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It is a cytochrome P450 enzyme, which belongs to the oxidoreductase class, and converts cholesterol to 7-alpha-hydroxycholesterol, the first and rate limiting step in bile acid synthesis. The inhibition of cholesterol 7-alpha-hydroxylase represses bile acid biosynthesis, the superfamily Cytochrome P450 was named in 1961, because of the 450-nm spectral peak pigment that cytochrome P450 has when reduced and bound to carbon monoxide. In the early 1960s, P450 was thought to be one enzyme, however, the membrane-associated and hydrophobic nature of the enzyme system impeded purification, and the number of proteins involved could not be accurately counted. Substrates identified to date include saturated and unsaturated fatty acids, eicosanoids, sterols and steroids, bile acids, vitamin D3 derivatives, retinoids, many cytochrome P450 enzymes can metabolise various exogenous compounds including drugs, environmental chemicals and pollutants, and natural plant products. The expression of many P450 enzymes is often induced by accumulation of a substrate, the ability of one P450 substrate to affect the concentrations of another in this manner is the basis for so-called drug-drug interactions, which complicate treatment. Cholesterol 7 alpha hydroxylase consists of 491 amino acids, which on folding forms 23 alpha helices and 26 beta sheets, cholesterol 7 alpha-hydroxylase is a cytochrome P450 heme enzyme that oxidizes cholesterol in the position 7 using molecular oxygen. CYP7A1 is located in the reticulum and is important for the synthesis of bile acid. Bile acids have powerful toxic properties like the membrane disruption and there are a range of mechanisms to restrict their accumulation in tissues. The discovery of farnesoid X receptor which is located in the liver, has opened new insights, bile acid activation of FXR represses the expression of CYP7A1 via, raising the expression of small heterodimer, a non-DNA binding protein. The increased abundance of SHP causes it to associate with liver receptor homolog -1, furthermore, there is an FXR/SHP-independent mechanism that also represses CYP7A1 expression. This FXR/SHP-independent pathway involves the interaction of bile acids with liver macrophages and these inflammatory cytokines, which include tumor necrosis factor alpha and interleukin-1beta, act upon the liver parenchymal cells causing a rapid repression of the CYP7A1 gene. Regulation of CYP7A1 occurs at several levels including synthesis, bile acids, steroid hormones, inflammatory cytokines, insulin, and growth factors inhibit CYP7A1 transcription through the 5′-upstream region of the promoter. The average life of this enzyme is between two and three hours, activity can be regulated by phosphorylation-dephosphorylation. CYP7A1 is upregulated by the nuclear receptor LXR when cholesterol levels are high, the effect of this upregulation is to increase the production of bile acids and reduce the level of cholesterol in hepatocytes. It is downregulated by Sterol regulatory element-binding proteins when plasma cholesterol levels are low, bile acids provide feedback inhibition of CYP7A1 by at least two different pathways, both involving the farnesoid X receptor, FXR. In the liver, bile acids bound to FXR induce Small heterodimer partner, SHP which binds to LRH-1, in the intestine, bile acids/FXR stimulate production of FGF15/19, which then acts as a hormone in the liver via FGFR4. One feature of enzymes is their high specificity and they are specific on a singular substrate, reaction or both together, that means, that the enzymes can catalyze all reactions wherein the substrate can experience. The enzyme cholesterol 7 alpha hydroxylase catalyzes the reaction that converts cholesterol into cholesterol 7 alpha hydroxylase reducing and oxidizing that molecule, click on genes, proteins and metabolites below to link to respective articles

7.
Enzyme
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Enzymes /ˈɛnzaɪmz/ are macromolecular biological catalysts. Enzymes accelerate, or catalyze, chemical reactions, the molecules at the beginning of the process upon which enzymes may act are called substrates and the enzyme converts these into different molecules, called products. Almost all metabolic processes in the cell need enzymes in order to occur at rates fast enough to sustain life, the set of enzymes made in a cell determines which metabolic pathways occur in that cell. The study of enzymes is called enzymology, enzymes are known to catalyze more than 5,000 biochemical reaction types. Most enzymes are proteins, although a few are catalytic RNA molecules, enzymes specificity comes from their unique three-dimensional structures. Like all catalysts, enzymes increase the rate of a reaction by lowering its activation energy, some enzymes can make their conversion of substrate to product occur many millions of times faster. An extreme example is orotidine 5-phosphate decarboxylase, which allows a reaction that would take millions of years to occur in milliseconds. Chemically, enzymes are like any catalyst and are not consumed in chemical reactions, enzymes differ from most other catalysts by being much more specific. Enzyme activity can be affected by other molecules, inhibitors are molecules that decrease enzyme activity, many drugs and poisons are enzyme inhibitors. An enzymes activity decreases markedly outside its optimal temperature and pH, some enzymes are used commercially, for example, in the synthesis of antibiotics. French chemist Anselme Payen was the first to discover an enzyme, diastase and he wrote that alcoholic fermentation is an act correlated with the life and organization of the yeast cells, not with the death or putrefaction of the cells. In 1877, German physiologist Wilhelm Kühne first used the term enzyme, the word enzyme was used later to refer to nonliving substances such as pepsin, and the word ferment was used to refer to chemical activity produced by living organisms. Eduard Buchner submitted his first paper on the study of yeast extracts in 1897, in a series of experiments at the University of Berlin, he found that sugar was fermented by yeast extracts even when there were no living yeast cells in the mixture. He named the enzyme that brought about the fermentation of sucrose zymase, in 1907, he received the Nobel Prize in Chemistry for his discovery of cell-free fermentation. Following Buchners example, enzymes are usually named according to the reaction they carry out, the biochemical identity of enzymes was still unknown in the early 1900s. Sumner showed that the enzyme urease was a protein and crystallized it. These three scientists were awarded the 1946 Nobel Prize in Chemistry, the discovery that enzymes could be crystallized eventually allowed their structures to be solved by x-ray crystallography. This high-resolution structure of lysozyme marked the beginning of the field of structural biology, an enzymes name is often derived from its substrate or the chemical reaction it catalyzes, with the word ending in -ase

8.
Nicotinamide adenine dinucleotide
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Nicotinamide adenine dinucleotide is a coenzyme found in all living cells. The compound is a dinucleotide, because it consists of two nucleotides joined through their phosphate groups, one nucleotide contains an adenine base and the other nicotinamide. Nicotinamide adenine dinucleotide exists in two forms, an oxidized and reduced form abbreviated as NAD+ and NADH respectively, in metabolism, nicotinamide adenine dinucleotide is involved in redox reactions, carrying electrons from one reaction to another. The coenzyme is, therefore, found in two forms in cells, NAD+ is an oxidizing agent – it accepts electrons from other molecules and becomes reduced and this reaction forms NADH, which can then be used as a reducing agent to donate electrons. These electron transfer reactions are the function of NAD. However, it is used in other cellular processes, the most notable one being a substrate of enzymes that add or remove chemical groups from proteins. Because of the importance of these functions, the involved in NAD metabolism are targets for drug discovery. In organisms, NAD can be synthesized from simple building-blocks from the amino acids tryptophan or aspartic acid, in an alternative fashion, more complex components of the coenzymes are taken up from food as the vitamin called niacin. Similar compounds are released by reactions that break down the structure of NAD and these preformed components then pass through a salvage pathway that recycles them back into the active form. Some NAD is also converted into nicotinamide adenine dinucleotide phosphate, the chemistry of this related coenzyme is similar to that of NAD, nicotinamide adenine dinucleotide, like all dinucleotides, consists of two nucleosides joined by a pair of bridging phosphate groups. The nucleosides each contain a ring, one with adenine attached to the first carbon atom. The nicotinamide moiety can be attached in two orientations to this carbon atom. Because of these two structures, the compound exists as two diastereomers. It is the diastereomer of NAD+ that is found in organisms. These nucleotides are joined together by a bridge of two groups through the 5 carbons. In metabolism, the compound accepts or donates electrons in redox reactions, such reactions involve the removal of two hydrogen atoms from the reactant, in the form of a hydride ion, and a proton. The proton is released into solution, while the reductant RH2 is oxidized, the midpoint potential of the NAD+/NADH redox pair is −0.32 volts, which makes NADH a strong reducing agent. The reaction is reversible, when NADH reduces another molecule and is re-oxidized to NAD+

9.
Limonene
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Limonene is a colorless liquid hydrocarbon classified as a cyclic terpene. The more common d-isomer possesses a strong smell of oranges and it is used in chemical synthesis as a precursor to carvone and as a renewables-based solvent in cleaning products. The less common l-isomer is found in mint oils and has a piney, limonene takes its name from the lemon, as the rind of the lemon, like other citrus fruits, contains considerable amounts of this compound, which contributes to their odor. Limonene is a molecule, and biological sources produce one enantiomer, the principal industrial source, citrus fruit, contains d-limonene. Racemic limonene is known as dipentene, d-Limonene is obtained commercially from citrus fruits through two primary methods, centrifugal separation or steam distillation. Limonene is a relatively stable terpene and can be distilled without decomposition and it oxidizes easily in moist air to produce carveol, carvone, and limonene oxide. With sulfur, it undergoes dehydrogenation to p-cymene, limonene occurs commonly as the d or -enantiomer, but racemizes to dipentene at 300 °C. When warmed with mineral acid, limonene isomerizes to the conjugated diene α-terpinene, evidence for this isomerization includes the formation of Diels-Alder adducts between α-terpinene adducts and maleic anhydride. It is possible to effect reaction at one of the double bonds selectively, anhydrous hydrogen chloride reacts preferentially at the disubstituted alkene, whereas epoxidation with mCPBA occurs at the trisubstituted alkene. In another synthetic method Markovnikov addition of trifluoroacetic acid followed by hydrolysis of the acetate gives terpineol, limonene is formed from geranyl pyrophosphate, via cyclization of a neryl carbocation or its equivalent as shown. The final step involves loss of a proton from the cation to form the alkene, the most widely practiced conversion of limonene is to carvone. The three step reaction begins with the addition of nitrosyl chloride across the trisubstituted double bond. This species is then converted to the oxime with base, d-Limonene applied to skin may cause irritation, but otherwise appears to be safe for human uses. Limonene is common in cosmetic products, as the main odor constituent of citrus, d-limonene is used in food manufacturing and some medicines, e. g. It is added to cleaning products such as hand cleansers to give a lemon-orange fragrance, in contrast, l-limonene has a piney, turpentine-like odor. In natural and alternative medicine, d-limonene is marketed to relieve gastroesophageal reflux disease, limonene is increasingly being used as a solvent for cleaning purposes, such as the removal of oil from machine parts, as it is produced from a renewable source. It is used as a paint stripper and is useful as a fragrant alternative to turpentine. Limonene is also used as a solvent in some model airplane glues, all-natural commercial air fresheners, with air propellants, containing limonene are used by philatelists to remove self-adhesive postage stamps from envelope paper

10.
Hydrogen ion
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A hydrogen ion is created when a hydrogen atom loses or gains an electron. A lone positively charged ion can readily combine with other particles. Due to its high charge density of approximately 2×1010 times that of a sodium ion. The hydrogen ion is recommended by IUPAC as a term for all ions of hydrogen. Depending on the charge of the ion, two different classes can be distinguished, positively charged ions and negatively charged ions, a hydrogen atom is made up of a nucleus with charge +1, and a single electron. Therefore, the positively charged ion possible has charge +1. In connection with acids, hydrogen ions typically refers to hydrons, Hydrogen atom contains a single proton and a single electron. Removal of the electron gives a cation, whereas addition of a gives a anion. The hydrogen anion, with its loosely held two-electron cloud, has a larger radius than the neutral atom, which in turn is much larger than the bare proton of the cation. Hydrogen forms the cation that has no electrons, but even cations that still retain one or more electrons are still smaller than the neutral atoms or molecules from which they are derived. This happens when hydrogen ions get pushed across the membrane creating a high concentration inside the thylakoid membrane, however, because of osmosis the H+ will force itself out of the membrane through ATP synthase. Utilizing their kinetic energy to escape, the protons will spin the ATP synthase which in turn will create ATP and this happens in cellular respiration as well though the concentrated membrane will instead be the inner membrane of the mitochondria. Hydrogen ions are also important in pH as they are responsible for if a compound is acidic or basic, water detaches to form H+ and hydroxides. This process is referred to as the self-ionization of water Acid Protonation Dihydrogen cation Trihydrogen cation Britannica Molecular Hydrogen Foundation

11.
Flavoprotein
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Flavoproteins are proteins that contain a nucleic acid derivative of riboflavin, the flavin adenine dinucleotide or flavin mononucleotide. The spectroscopic properties of the flavin cofactor make it a natural reporter for changes occurring within the active site, flavoproteins have either an FMN or FAD molecule as a prosthetic group, this prosthetic group can be tightly bound or covalently linked. Only about 5-10% of flavoproteins have a covalently linked FAD, in some instances, FAD can provide structural support for active sites or provide stabilization of intermediates during catalysis. Based on the structural data, the known FAD-binding sites can be divided into more than 200 different types. There are 90 flavoproteins in the genome, about 84% require FAD. Flavoproteins are mainly located in the mitochondria because of their redox power, of all flavoproteins, 90% perform redox reactions and the other 10% are transferases, lyases, isomerases, ligases. By the early 1930s, this same pigment had been isolated from a range of sources and its structure was determined almost simultaneously by two groups in 1934, and given the name riboflavin, derived from the ribityl side chain and yellow colour of the conjugated ring system. The first evidence for the requirement of flavin as an enzyme cofactor came in 1935, neither apoprotein nor pigment alone could catalyse the oxidation of NADH, but mixing of the two restored the enzyme activity. However, replacing the isolated pigment with riboflavin did not restore enzyme activity, the flavoprotein family contains a diverse range of enzymes, including, Epidermin biosynthesis protein, EpiD, which has been shown to be a flavoprotein that binds FMN. This enzyme catalyses the removal of two reducing equivalents from the residue of the C-terminal meso-lanthionine of epidermin to form a --C==C-- double bond. The B chain of dipicolinate synthase, an enzyme which catalyses the formation of acid from dihydroxydipicolinic acid. It compares the structures to elucidate phylogenetic relationships. This article incorporates text from the public domain Pfam and InterPro IPR003382

The energies of the stages of a chemical reaction. Uncatalysed (dashed line), substrates need a lot of activation energy to reach a transition state, which then decays into lower-energy products. When enzyme catalysed (solid line), the enzyme binds the substrates (ES), then stabilizes the transition state (ES‡) to reduce the activation energy required to produce products (EP) which are finally released.